This research proposal contains two cross cutting themes. In the first theme, new experimental methods will be used that allow investigations to move beyond questions of what infants and animals know to how they know. By using modified versions of methods that have been used with human adults since the 1960's (i.e. chronometry), it will be possible to study the mental processes and cognitive systems underlying specific types of knowledge in infants and animals. Furthermore, by studying human infants and non-human primates with the same methods, it will be possible to investigate which of the mental processes and cognitive machinery that are available to human infants come from their human specific genetic endowment, and which are shared with other animals and thus evolutionary ancient. The second theme proposes: (1) chronometric studies investigating the mental processes by which individual objects, sets of objects, and representations of number are constructed, and (2) interference studies investigating the processes and cognitive machinery underlying representations of diverse types of individuals.